Method of producing titanium and titanium alloy nanopowder from titanium-containing slag through shortened process

ABSTRACT

Disclosed is a method of producing titanium and titanium alloy nanopowder from titanium-containing slag through a shortened process. The method includes: (1) subjecting titanium-containing slag to high-temperature oxidation and enrichment and then melting to precipitate titanium-enriched slag; (2) subjecting the titanium-enriched slag to pulverization and gravity flotation; (3) carrying out secondary enrichment; (4) preparing a molten salt reaction system; (5) synthesizing titanium and salt-containing titanium alloy nanopowder by reduction reaction; and (6) vacuum filtering, pickling, washing and vacuum drying the salt-containing titanium alloy nanopowder; and then separating titanium alloy nanopowder from the molten salt. Using the present method, the titanium-containing slag can be continuously treated to produce titanium and titanium alloy nanopowder. It requires a shortened process, a simple equipment and low energy consumption. The process is environmentally friendly and produces excellent products without solids, gas or liquids that are harmful to environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from Chinese Application No. 201811396542.X, filed on Nov. 22, 2018. The contents of the aforementioned application, including any intervening amendments thereto, are incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to metallurgical engineering, and more specifically to a method of producing titanium and titanium alloy nanopowder from titanium-containing slag through a shortened process.

BACKGROUND

Titanium and titanium alloy, known as “modern metal” and “strategic metal”, are very important strategic materials to industry application. Because of their low specific gravity, high intensity, corrosion resistance and good biocompatibility, titanium and titanium alloy can meet the higher requirements of new super alloy materials in high-tech industries such as aerospace, biomedical science, transportation and communication. Titanium and titanium alloy materials have become research focus on super alloy materials.

China has the world's first titanium resource. Scientists and engineers in recent years have developed two main methods for integrated utilization of vanadium-titanium magnetite: (1) a blast furnace smelting process^([1]); and (2) a rotary hearth furnace-electric arc furnace direct reduction process^([2-4]) including titanium hydrometallurgical and pyrometallurgical processes.

The blast furnace smelting process for integrated utilization of vanadium-bearing titanomagnetite uses vanadium-bearing titanomagnetite from Chengde as raw materials. Iron concentrate after magnetic separation is smelted in a blast furnace to obtain vanadium-containing molten iron and blast furnace slag with 20 wt. % of TiO₂. In addition, the tailing after beneficiation undergoes strong magnetic separation to obtain ilmenite and electric furnace smelting to obtain high-titanium slag followed by hydrometallurgical combined with conventional Kroll method to produce titanium dioxide/titanium sponge. This process can significantly extract and recycle vanadium but with low titanium recycling. Also, the process itself has shortcomings such as long process, complicated operation and equipment, and being environmentally unfriendly, which directly affects the integrated utilization of vanadium-titanium magnetite and economic cost.

In the rotary hearth furnace-electric arc furnace direct reduction process for integrated utilization of vanadium-bearing titanomagnetite, iron concentrate and ilmenite are pre-reduced in the rotary hearth furnace after weak magnetic separation and strong magnetic separation, and then are melted in the electric arc furnace to obtain vanadium-containing molten iron and titanium-enriched slag. The conversion rate of titanium dioxide from titanium is 65%, and the grade of TiO₂ in the titanium-containing slag reaches 40%-50%^([5-6]). Although this process increases the recycling of titanium, the grade of TiO₂ is lower compared to the high-titanium slag. In the production of titanium dioxide, there exists a complicated process, a long production cycle, large acid consumption and difficulty in the treatment of waste acid, which greatly limits the wide application of such process^([7-9]).

To solve the above problems existing in the process of producing titanium dioxide from titanium-containing slag, Zhitong Sui et al.^([10]) propose “A selective enrichment-mineral separation process”. In this process, titanium in the lean slag is reconstructed into perovskite to obtain a product enriched with titanate or titanium oxide through oxidation and enrichment at high temperature, melting, precipitation and gravity flotation. This process simplifies operation and reduces equipment costs, acid consumption and pollution to the environment. However, this process still has problems such as cumbersome operation, complicated equipment and environmental pollution in the production of titanium products from titanate or titanium oxide. Professor Homgmin Zhu^([11-14]) proposes a USTB process of synthesizing TiC_(x)O_(y) as an intermediate at high temperature using the mineral phase reconstruction process and then electrolysis in molten salt to obtain titanium. Although the USTB process makes great breakthrough in theory, some problems in the industrial application still remain unsolved.

A molten salt metal thermal reduction method produces a metal element or an alloy material through the metal thermal reduction in molten salt medium^([15-17]). This method has short process, low energy consumption and simple equipment and is environmentally friendly in the production of refractory metals and alloy materials (or intermetallic compounds). Okabe et al.^([18]) propose a process for producing niobium powder with purity of more than 99.5% by adding CaCl₂ after magnesiothermic reduction of Nb₂O₅. Ryosuke et al.^([19]) study a method for producing niobium powder in CaCl₂ molten salt medium containing saturated calcium by calciothermic reduction of Nb₂O₅. Shekhter et al.^([20]) discuss a method for reducing powdered rare metal oxide in melted CaCl₂ molten salt medium through Ca or Mg steam. Baba et al.^([21]) study reaction time of a method for producing niobium powder in CaCl₂ molten salt medium by calciothermic reduction of Nb₂O₅. The molten salt calciothermic reduction method can produce high-purity niobium nanopowder from direct reduction of Nb₂O₅ powder (or conceptus) by Ca steam to direct reduction of Nb₂O₅ by Ca atom in molten salt diluent. Later, Hongmin Zhu et al.^([15-17]) do a series of researches on producing niobium and niobium-aluminium intermetallic compounds in CaCl₂ molten salt medium through sodiothermic reduction to obtain niobium and Nb₃A/NbAl₃/Nb₂Al—NbAl₃ nanopowder. Na Wang et al.^([22-23]) do a series of researches on recycling cemented carbide powder in CaCl₂ molten salt medium through sodiothermic reduction in detail, successfully recycling and regenerating W/WC/WC—Co cemented carbide powder.

SUMMARY

To overcome the shortcomings in the prior art, the present application provides a method of producing titanium and titanium alloy nanopowder from titanium-containing slag through a shortened process. The method includes:

1) mixing titanium-containing slag A with a modifier B in a reaction vessel; heating the reaction vessel to a reacting temperature for oxidation and enrichment, titanium in the titanium-containing slag A being formed into TiO₃ ²⁻ by the modifier B; and then cooling to precipitate titanium-enriched slag containing titanate C;

2) subjecting the titanium-enriched slag obtained in step 1) to pulverization, gravity flotation and drying to separate the titanium-enriched slag from other impure ores;

3) repeating steps 1) and 2) to improve purity of the titanate C as an intermediate;

4) mixing the titanate C obtained in step 3) with a molten salt medium; dehydrating under vacuum and then melting at 550-900° C. to form a molten salt reaction system, titanium in the the mixture being formed into TiO₃ ²⁻;

5) adding a reducing agent into the molten salt reaction system obtained in step 4) for thermal reduction in an inert gas at 400-900° C. to synthesize titanium and salt-containing titanium alloy nanopowder; and

6) vacuum filtering, pickling, washing and vacuum drying the salt-containing titanium alloy nanopowder obtained in step 5); and then separating the titanium alloy nanopowder from the salt-containing titanium alloy nanopowder to obtain titanium and titanium alloy nanopowder.

Preferably, in step 1) the modifier B is selected from one or more of Na₂O, CaO, K₂O, NaOH, Ca(OH)₂, KOH, Na₂CO₃, Ca₂CO₃ and K₂CO₃.

Preferably, in step 1) the titanate C is selected from one or more of Na₂TiO₃, CaTiO₃, K₂TiO₃ and TiO₂.

Preferably, in step 1) the oxidation and enrichment is carried out at a temperature of 1100-1500° C. for 5-10 hours.

Preferably, in step 2) the titanium-enriched slag is pulverized to 100-300 mesh and the drying is carried out at 100-300° C.

Preferably, in step 4) a vacuum degree is 0.2-0.3 MPa. A mole percentage of the titanate C is 1-10 mol %. The molten salt medium includes a compound D having a mole percentage of 50-100 mol % and a compound E having a mole percentage of 0-40 mol %, and the dehydrating temperature is 150-350° C.

Preferably, in step 5) the reducing agent is selected from sodium, calcium or magnesium. The inert gas is argon at a flow rate of 1-30 mL/s.

Preferably, in step 6) a vacuum degree is 0.2-0.5 MPa, and a vacuum drying temperature is 30-50° C.

Preferably, the compound D is selected from one or more of CaCl₂, NaF and KF, and the compound E is selected from one or more of NaCl, KCl, LiCl and NaAlO₂.

Preferably, the oxidation and enrichment is carried out at 1200-1400° C.

Preferably, the reduction and synthesis is carried out at 1200-1400° C.

The present disclosure has the following advantages:

1. Titanium in titanium-containing slag is formed into TiO₃ ²⁻ in the intermediate by the modifier at high temperature, and the intermediate and other raw materials are melted in molten salt to form a uniform reaction system. Then, the reaction system is reduced and synthesized into titanium and titanium alloy powder under the action of the reducing agent. The particle size of titanium alloy powder is 50-1000 nm, and the purity is more than 98.5 wt %. The present disclosure can continuously treat titanium-containing slag to prepare titanium and the titanium alloy powder materials which can be used as raw materials for spray painting, powder metallurgy and 3D printing, and can be widely applied in high-tech industries including aerospace, military industry, biomedical field and traffic information.

2. The present disclosure over the existing titanium alloy production process has short process, simple equipment, low energy consumption, green production and excellent products without producing solid/gas/liquid harmful substances, and can create enormous economic and social benefits. The present disclosure can also be applied in the production of refractory metals and theirs alloys, rare earth metals, intermetallic compounds and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be further described in detail with reference to the accompanying drawings and embodiments.

FIG. 1 is a flow chart showing a method according to the present invention.

FIG. 2 is a schematic diagram showing X-ray Diffraction (XRD) pattern of phase analysis on Ti nanopowder prepared in Example 1 according to the present invention.

FIG. 3 is a Field Emission Scanning Electron Microscopy (FESEM) image showing surface appearance of Ti nanopowder prepared in Example 1 according to the present invention.

FIG. 4 is a schematic diagram of XRD pattern of phase analysis on Ti—Al alloy nanopowder prepared in Example 2 according to the present invention.

FIG. 5 is an FESEM image showing surface appearance of Ti—Al alloy nanopowder prepared in Example 2 according to the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The present disclosure is further described with reference to the following embodiments.

The present disclosure may adopt the conventional devices in the art for extraction, reduction and synthesis of titanium-containing slag through a short process. The following embodiments are carried out using the process shown in FIG. 1.

EXAMPLE 1

This embodiment illustrates a method of preparing Ti nanopowder using ilmenite (grade: 52%) through reduction reaction. 200 g of ilmenite and 33 g of CaO were uniformly mixed, and then pressed into a block and placed in a high-temperature furnace for oxidation and enrichment at 1350° C. for 7 hours. They were cooled to precipitate and were pulverized into powder having a size of 200 mesh when cooled to room temperature. The powder was subjected to gravity flotation to obtain titanium-enriched slag. The titanium-enriched slag was subjected to the secondary oxidation and enrichment at 1250° C. for 5 hours to obtain titanate (CaTiO₃) as an intermediate during which a ratio of the titanium-enriched slag to CaO is 90:10 by weight. The intermediate was then mixed with a molten salt medium containing NaCl-60 mol %CaCl₂ in a ratio of 10:90 by weight. The mixture was melted in a reaction furnace at 750° C. to form a molten salt reaction system. Calcium as a reducing agent was added for reduction for 6 hours to synthesize Ti nanopowder. After the reaction was completed, the furnace was decreased to room temperature. The calciothermic reduction is carried out under the protection of Ar gas. Finally, the resulting Ti nanopowder and the molten salt were washed in 3-5% dilute hydrochloric acid and distilled water, and then were filtered and vacuum dried at 35° C. with a vacuum degree of 0.4 MPa to separate the Ti nanopowder from the molten salt.

The purity of the prepared Ti nanopowder reaches 98.45 wt %. The particle size of the spherical agglomerated particles ranges from 100 to 250 nm. The XRD pattern of phase analysis and FESEM image of Ti nanopowder are shown in the FIGS. 2 and 3, respectively.

EXAMPLE 2

This embodiment illustrates a method of preparing Ti—Al alloy nanopowder using ilmenite (grade: 50%) through reduction reaction. 200 g of titanium concentrate and 52 g of CaCO₃ were uniformly mixed, and then pressed into a block and placed in a high-temperature furnace at 1450° C. for oxidation and enrichment for 8 hours. They were cooled to precipitate and was pulverized into powder having a size of 200 mesh when cooled to room temperature. The powder was subjected to gravity flotation to obtain titanium-enriched slag. The titanium-enriched slag was subjected to the secondary oxidation and enrichment at 1350° C. for 6 hours to obtain titanate (CaTiO₃) as an intermediate during which a ratio of the titanium-enriched slag to CaCO₃ is 80:10 by weight. The intermediate was then mixed with a molten salt medium containing sodium aluminate and NaCl-52 mol % CaCl₂ in a ratio of 6:4:90 by weight. The mixture was melted in a reaction furnace at 700° C. to form a molten salt reaction system. Sodium as a reducing agent was added for reduction for 8 hours to synthesize Ti—Al alloy nanopowder. After the reaction is completed, the furnace is cooled to room temperature, and the calciothermic reduction is carried out under the protection of Ar gas. Finally, the resulting Ti—Al alloy nanopowder and the molten salt were washed in 3-5% dilute hydrochloric acid and distilled water, and then were filtered and vacuum dried at 35° C. with a vacuum degree of 0.4 MPa to separate the Ti—Al alloy nanopowder from the molten salt.

The purity of the prepared Ti—Al alloy powder reaches 99.32 wt %. The particle size of spherical agglomerated particles ranges from 150 to 450 nm. The XRD pattern of phase analysis and FESEM image of Ti—Al alloy nanopowder are shown in FIGS. 4 and 5, respectively.

The above embodiments are only illustrative of the present invention, and the present invention is not limited thereto. It should be understood that any variations and modifications made by those skilled in the art within the spirit of the invention shall fall into the scope of the present disclosure.

REFERENCE LIST

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What is claimed is:
 1. A method of producing titanium and titanium alloy nanopowder from titanium-containing slag through a shortened process, comprising: 1) mixing titanium-containing slag A with a modifier B in a reaction vessel; heating the reaction vessel to a reaction temperature for oxidation and enrichment, titanium in the titanium-containing slag A being formed into TiO₃ ²⁻ by the modifier B; and then cooling to precipitate titanium-enriched slag containing titanate C; 2) subjecting the titanium-enriched slag obtained in step 1) to pulverization, gravity flotation and drying to separate the titanium-enriched slag from other impure ores; 3) repeating steps 1) and 2) to improve purity of the titanate C as an intermediate; 4) mixing the titanate C obtained in step 3) and a molten salt medium; dehydrating under vacuum and then melting at 550-900° C. to form a molten salt reaction system, titanium in the mixture being formed into TiO₃ ²⁻; 5) adding a reducing agent into the molten salt reaction system obtained in step 4) for thermal reduction in an inert gas at 400-900° C. to synthesize titanium and salt-containing titanium alloy nanopowder; and 6) vacuum filtering, pickling, washing and vacuum drying the salt-containing titanium alloy nanopowder obtained in step 5); and then separating the titanium alloy nanopowder from the salt-containing titanium alloy nanopowder to obtain titanium and titanium alloy nanopowder.
 2. The method of claim 1, wherein in step 1) the modifier B is selected from one or more of Na₂O, CaO, K₂O, NaOH, Ca(OH)₂, KOH, Na₂CO₃, Ca₂CO₃ and K₂CO₃.
 3. The method of claim 1, wherein in step 1) the titanate C is selected from one or more of Na₂TiO₃, CaTiO₃, K₂TiO₃ and TiO₂.
 4. The method of claim 1, wherein in step 1) the oxidation and enrichment is carried out at a temperature of 1100-1500° C. for 5-10 hours.
 5. The method of claim 1, wherein in step 2) the titanium-enriched slag is pulverized to 100-300 mesh, and the drying is carried out at 100-300° C.
 6. The method of claim 1, wherein in step 4), a vacuum degree is 0.2-0.3 MPa; a mole percentage of the titanate C is 1-10 mol %; the molten salt medium comprises a compound D having a mole percentage of 50-100 mol % and a compound E having a mole percentage of 0-40 mol %; and a dehydrating temperature is 150-350° C.
 7. The method of claim 1, wherein in step 5) the reducing agent is selected from sodium, calcium or magnesium, and the inert gas is argon at a flow rate of 1-30 mL/s.
 8. The method of claim 1, wherein in step 6) a vacuum drying temperature is 30-50° C., and a vacuum degree is 0.2-0.5 MPa.
 9. The method of claim 6, wherein the compound D is selected from one or more of CaCl₂, NaF and KF; and the compound E is selected from one or more of NaCl, KCl, LiCl and NaAlO₂. 